(A) urbs1 locus of U. maydis. Horizontal arrow represents the urbs1 open reading frame (ORF). Restriction sites: A, AsuII; B, BamHI; BI, BglII; H, HindIII; P, PstI; S, StuI; X, XbaI. (B) Epitope-tagged urbs1 alleles. pAN15 contains the wild-type allele. pAN15–1, pAN15–2, and pAN15–3 contain the NTG-induced urbs1 mutations contained in the 2-kb StuI fragment from UMC002, UMC005, and UMC007, respectively. pAKR494L and pAKR350L contain single amino acid mutations introduced via site-directed mutagenesis.